The advent of the ability to establish a voice call over the Internet, colloquially called “VoIP” and pronounced “VoIP” has well-known advantages, but it will be some years before the Public Switched Telephone Network is completely displaced by VoIP. During the transition, however, people will desire to initiate a voice call on the Public Switched Telephone Network (“PSTN”) to a VoIP telephone on the Internet. There is problem developing with doing this, however, which is illustrated in FIGS. 1 and 2 and the accompanying text.
FIG. 1 depicts a schematic diagram of the salient components of a telecommunications system in the prior art in which a voice call on the Public Switched Telephone Network terminates at a VoIP telephone on the Internet. System 100 comprises PSTN telephone 101, VoIP telephone 102, switching network 111, PSTN/VoIP gateway 112, and dynamic name system server 113. Both PSTN telephone 101 and VoIP telephone 102 are associated with a unique telephone number so that they can called.
FIG. 2 depicts a flowchart of the salient tasks in the prior art associated with the establishment of a voice call that begins at a telephone in the Public Switched Telephone Network and terminate as a VoIP call on the Internet.
At task 201, a call is initiated from PSTN telephone 101 to VoIP telephone 102, by dialing the telephone number of VoIP telephone 102.
At task 202, switching network 111 knows from its directory table that VoIP telephone 102 is reachable via PSTN/VoIP gateway 112, and, therefore, switching network 111 transmits a call set-up message to PSTN/VoIP gateway 112. The call set-up message comprises the telephone number of VoIP telephone 102.
At task 203, PSTN/VoIP gateway 112 finds the current IP address of VoIP telephone 102 from the telephone number of VoIP telephone 102 by converting the telephone number into a dynamic name system address and by transmitting the dynamic name system address to dynamic name system server 113.
At task 204, PSTN/VoIP gateway 112 receives the current IP address of VoIP telephone 102 from dynamic name system server 113.
At task 205, PSTN/VoIP gateway 112 attempts to establish a voice call with VoIP telephone 102 at the IP address received in task 204.
The problem with this technique is that VoIP telephone 102 must have a unique telephone number. As the number of VoIP telephones increases, the number of newly issued telephone numbers also increases, which is expensive. The need exists, therefore, for a technique for establishing a voice call on the Public Switched Telephone Network to a VoIP telephone on the Internet without the association of a unique telephone number to the telephone.